The centrifugal-type refrigeration equipment is known to be different in features with the volumetric compression-type refrigeration equipment. Currently, the control method upon capacity of a centrifugal water-chilling set is mainly to control the inlet guide vane (IGV) at the air inlet of the centrifugal compressor so as to regulate the loads and thereby to adjust the capacity of the water-chilling set. However, while the centrifugal water-chilling set is operated at a low loading condition or under a condition with an increasing pressure difference between the high and the low pressures, since the mass flow rate of the refrigerant cannot overcomes the pressure difference, the refrigerant flow is hard to reach the high-pressure end, and thus an unexpected stop in refrigerant flow is thus inevitable. Then, the gas at the high-pressure end would flow reversely back to the low-pressure end. As soon as the pressure at the low-pressure end is increased, namely while the pressure difference is reduced, the compressor vane may then resume its compression operation. At this time, the refrigerant flow backs to the normal flow, and the pressure difference rises again. In the case that the pressure difference rises to a value exceeding the compressible margin of the vane, the refrigerant gas at the high-pressure end would then flow reversely back to the low-pressure end again. Such a cycle repeating again and again is the so-called surging of the compressor.
The surging is specifically seen in the centrifugal machines. To avoid the surging, the conventional centrifugal-type water-chilling set usually bypass the high-pressure gas to the low-pressure end, such that the centrifugal-type water-chilling set can keep operated at the low loading condition without possible surging, and thus related damages to the compressor can be substantially reduced.
As described, the capacity adjustment of the centrifugal compressor is firstly to control the throttle percentage of the IGV while the load is reduced. As the minimum throttle percentage is already reached but the load keeps decreasing, the gas bypass is then opened so as to adjust the pressure and so as further to inhibit surging.
In the art, the IGV and the bypass structure in a centrifugal compressor are both isolated. In particular, the IGV is constructed inside the compressor, while the bypass structure is constructed to connect the exhaust pipe and the bypass pipe; in which the exhaust is to connect the outlet of the compressor and the condenser, and the bypass pipe is to connect the inlet of the compressor and the evaporator.
One of disadvantages in the aforesaid arrangement for separately constructing the IGV and the bypass structure is obvious the increased complexity of the piping for the compressor. Further, it is also required to establish individually a driving motor assembly and a controller to perform the driving and the control.